Tar and Pitch

This article discusses the origins of tars and pitches from the pyrolysis of organic matter in general; those derived from coal are dealt with in detail. The physical characteristics of tars and pitch residues are summarized, as are the chemical composition of the fractions produced and the distillation processes by which they are obtained from coal tar. Change has taken place in the twentieth century in the role of coal tar as the principal source of aromatic organic chemicals, and for road construction and surfacing, which has become an important source of components for carbon products, binders, and coating materials. Attention is drawn to the remaining chemical products of commercial importance, principally naphthalene, creosote oil, anthracene, and modest amounts of phenols and aromatic bases. There have also been a few newer uses for naphthalene and a novel purification process, as well as different requirements for pitches used as carbon binders and for the composition of creosote. Concern about the health and safety aspects of coal-derived substances has been considered by the authorities, particularly in the European Union and directives, and regulations have been introduced to reduce risks in both the environment and workplace. Keywords: Tar; Pitch; Wood tar; Coal tar; Dyes; Creosote; Fluxed pitches; Tar distillation; Coumarone-indene resins; Refined tars; Naphthalene; Roofing materials